Thermometric method of locating the top of the cement behind a well casing



Aug. 4, '1936. V c. SCHLUMBERGER 2,050,128

THERMOMETRIC METHOD OF LOCATING THE TOP OF'THE C NT BEHIND A WELL CASING ed May 24, 1934 v Patented Aug. 4, 1936 UNITED ST-AT'E THERMOMETRIC METHOD OF LOCATING THE TOP OF THE CEMENT BEHIND A WELL CASING Conrad Schlumberger, Paris, France, assignor', by mesne assignments, to Schlumbcrger Well Surveying Corporation, Houston, Tex., a corporation of Delaware Application May 24, 1934, Serial No. 727,358 In France March 30, 1934 (Cl. 166-21) V J 12 Claims.

the bottom of the hole in the annular space between the casing and the formation and, filling up this space, cements the lining to the surrounding beds. The quantity of cement injected is so calculated that the cement will rise up to the desired level and in particular will seal off the upper water-bearing strata. The block of cement remaining in the bottom of the bore hole is then drilled for bringing the oil-bearing bed into production.

Now, up to the present no means has been available for determining with any accuracy the level to which the cement has actually risen.

It has been found in accordance with the present invention that it is possible to determine this level by carrying out during the setting period of'the cement or immediately afterwards temperature measurements over the whole depth of the hole. It is known in fact that the setting of cement is accompanied by a liberation of heat, the intensity of which depends on the time which has elapsed since the mixing of the cement, on the nature of the latter, on the temperature of the surrounding medium, on the pressure, on the excess of water, and so on. It has been found that at the height of the upper level reached by the cementing fluid there is a very definite and substantial change in temperature which may be as much as from 1 to 10 C., the lower cemented part being at a higher temperature than the part above the cement. Consequently, if a continuous diagram of temperature 45 in terms of depth is made there would appear on this diagram a disturbance corresponding to the change in question, opposite to which one can read the depth at which the top of the cemented zone is located.

Preferably the temperature measurements will be effected as soon as possible after carrying out the cementing job. Nevertheless the heat generated by the setting of the cement generally persists for several days as a consequence. of the time necessary for the operation to be completed and also because the exchanges of heat are slow. Therefore a thermometric diagram may be taken several days after the completion of the cementing job and still exhibit a very marked irregularity at a point corresponding to the upper level 5 of the cemented zone.

As a further feature the method according to the invention may be used to reveal any irregularities in the cementing job, such as zones of excessive thickness or of insufficient thickness of cement, or irregularities in the process of hardening. In the former case there are local excesses of heating shown by a higher temperature than in the neighbouring zones; in the latter case there will be observed, on the contrary, a lower temperature.

In order to register the temperature diagram different methods of thermometric measurement may be employed. By way of example a particularly practical method would be the use of 20 an electrical resistance thermometer. Into the bore hole filled with water there is lowered a thermometric coil connected to the lower end of a cable of which the upper part is wound on a winch located at the surface of the ground. The electrical connections of this thermometric coil to the insulated conductors comprising the cable are so arranged that one can measure its electrical resistance from the ground level. Since this resistance depends upon the temperature it is then possible, after previous calibration of the apparatus, to determine the value of the temperature in the hole at the depth at which the coil is located. The presence of the water, which fills the hole, facilitates the making of the temperature measurements of the thermometric coil. It is advantageous to carry out these measurements in a continuous manner with an automatic apparatus as the arrangement is lowered in the hole. There is thus obtained a continuous record of the temperature down the bore hole in the form of a diagram on which the discontinuity corresponding to the top of the cementing will be indicated.

The accompanying drawing serves to illustrate the invention by means of an example, and therein:

Figure 1 is a diagrammatic section of a bore hole which has just been cemented and filled with water, and into which an electrical device has been lowered for thermometric measurements, and

Figure 2 shows the corresponding temperature diagram.

In the first figure, l represents the metallic casing lowered into the borehole to the level of the impervious stratum 2 nearest to the 011 hearing stratum 3 which is to be exploited. The cementing fluid 4 is pumped under pressure so as to fill up the annular space 5 remaining between the casing l and the wall of the hole and to seal of! the water bearing porous strata such as 6. After the cement mass 4 at the bottom of the hole has hardened it is drilled, as indicated by broken lines, for the purpose of bringing the oil bearing stratum into production.

In accordance with the invention, in order to determine the height which the top I of the cementing has reached, continuous thermometric measurements are taken in the water over the whole depth of the hole by means, for example, of a thermometric coil 8. The latter is connected to an insulated cable 9 which runs off a winch H];- the variations of the resistance of the coil 8 corresponding to the variations of temperature within the hole are recorded by a suitable apparatus i.

The diagram of temperature obtained is shown in Figure 2 and exhibits at the depth of the top I of the cementing zone a discontinuity i2 separating curve l3 of the warmer cemented region and curve 14 of the cooler uncemented region. In the example shown the diagram also exhibits another irregularity IE5 at a place corresponding to an excess of thickness N5 of cementing material, which makes itself evident by a. local temperature anomaly.

What I claim is:

1. In the process of lining a drill hole with cement, the steps of forcing a mass of fluid cement upwardly and in contact with the surface of said hole and making temperature measurements at different depths within the cement-lined portion of said hole during the heat-emission period of the cement.

2. In the process of lining a drill hole with cement-the steps of introducing into said hole a tubular casing such as to form an annular space between it and the surface of said hole, forcing cement into said space, and making temperature measurements within said casing during the heatemission period of the cement.

3. In the process of lining a drill hole with cement, the steps of introducing into said hole a tubular casing such as to form an annular space between it and the surface of said hole, forcing fluid cement upwardly into said space and making temperature measurements within said casing during the heat-emission period of the cement from which can be deduced data such as the location of the upper level of the cement.

4. In the process of lining a drill hole with cement, the steps of forcing a mass of fluid cement upwardly and in contact with the surface of said hole, filling said hole with water and making temperature measurements at various depths within the cement-lined portion of said hole during the heat-emission period of the cement.

5. In the process of lining a drill hole with cement, the steps of introducing into said hole a tubular casing such as to form an annular space between it and the surface of said hole, forcing cement into said space, filling said hole with water and making temperature measurements within said casing during the heat-emission period of the cement.

6. In the process of lining a drill hole with cement, the steps of forcing a mass of fluid cement-upwardly and in contact with the surface of said hole, making temperature measurements at various depths within the cement-lined portion 5 of said hole during the heat-emission period of the cemeht, and tracing a continuous diagram of temperature in terms of depths, thereby determining conditions of the encased cement such as the upper level thereof, or irregularities in thickness, or irregularities in the process of hardening.

7. In the operation of applying a cement lining to a drill hole and within a metalic casing, the method of determining the upper level reached by the cementing fluid behind said casing, which 15 method consists in making temperature measurements at various depths within said hole during the heat-emission period of the cement, thereby locating the abrupt change of temperature occur ring at said level.

8. In the operation of applying a cement lining to a drill hole and within a metallic casing, the method of determining the upper level reached by the cementing fluid behind said casing, which method consists in making temperature measurements at various depths within said hole during the heat-emission period of the cement and tracing a continuous diagram of temperature in terms of depth, thereby locating the abrupt change of temperature occurring at said level.

9. In the process of forming a cement structure by the pouring of fluid cement in a place underground and inaccessible to direct observation, the step of making a series of temperature measurements at points adjacent to the surface of 35 the mass of cement during the heat-emission period thereof.

10. In the process of forming a cement structure by the pouring of fluid cement in a place underground and inaccessible to direct observation, the steps of making a series of temperature measurements at points adjacent to the surface of the mass of cement but out of contact therewith during the heat-emission period thereof and tracing thereby a continuous diagram of temperature in terms of distance.

11. In the operation of pouring fluid cement into an open hole, the steps of forcing said cement against the wall of said hole; forming a cement plug which closes the lower end of said hole; drilling said plug; filling said hole with water; and making in said water temperature measurements at various depths within the cemented portion of said hole during the heat emission period of the cement.

12. In the operation of pouring fluid cement into an open hole, the steps of forcing said cement against the wall of said hole; forming a cement plug which closes the lower end of said hole; drilling said plug; filling said hole with 60 water; making in said water temperature measurements at various depths within the cemented portion of said hole during the heat emission period of the cement; and tracing a continuous diagram of temperature in terms of depth, thereby determining conditions of cementation of the uncased part of the hole such as irregularities and rate oi penetration of the cement in the porous formations traversed.

CONRAD SCI-ILUNIBERGER. 

